Before 1900, Henry Ford and Thomas Edison worked with each other to introduce an electric car. But gasoline powered engines soon prevailed over the electric motor and became the engines upon which a huge automobile industry was based. As compared to battery powered cars, gasoline fuel was cheaper, easier to distribute, had more energy content per kilogram, and was to become available in abundant supplies. But the electric car was not forgotten. Throughout the twentieth century, there have been periodic attempts to introduce electric vehicles. These tended to happen especially during periods of predicted energy shortages and threatened high fuel prices, when the search for alternatives took place. Until recently none of those efforts produced a viable commercial vehicle. Today, however, the interest in electric vehicles has experienced an unprecedented resurgence, fueled no doubt by recent concerns about global warming and renewed fears about the high costs of gasoline. Now there are hundreds of companies big and small designing and building electric vehicles, some of which have already made their way into the commercial mass markets.
Many of the current engine designs are based on rotary electric motors among which there are at least three general types: the DC motor, the synchronous AC motor, and the induction motor. A DC motor includes stationary permanent magnets in the stator and rotating electrical magnets in the form of coils on the rotor. Current is applied the electrical magnets on the rotor through a commutation ring and the magnetic fields produced by the permanent magnets interact with the current flowing through the coils to produce torque on the rotor. The AC induction motor typically includes a stationary electromagnetic stator and a rotating electromagnetic rotor. The rotating magnetic field pattern that is produced by the stator induces currents in the electromagnetic coils on the rotor. The induced currents in the rotor coils, in turn, interact with the rotating fields of the stator to cause rotational motion of the rotor. The AC synchronous motor, in contrast, has a permanent magnet rotor and electromagnets in the form of coils wound on the stator. Rotating magnetic fields are generated by driving the stator coils with time varying drive currents. The rotating magnetic fields produced by the stator cause the rotor to turn at the rate at which the fields are rotating.
A design that has emerged recently is based on the Lorentz-type actuator motor or linear motor. Unlike the other above-mentioned motors which directly produce torque through the motor's rotor shaft, the linear motor produces a linear back-and-forth movement of an actuator coil. That linear back-and-forth movement is then converted to rotary motion though interaction with a cam. The details of one such design is presented in U.S. Ser. No. 12/590,495, filed Nov. 9, 2009, and incorporated herein by reference.
The present application describes an improved design for the stator assembly in such a linear motor.